1. Field of the Invention
The present invention relates to a high-power gas laser oscillator device such as a machining CO.sub.2 laser or the like, and more particularly, to a gas laser oscillator device provided with an improved turbo blower for use in a CO.sub.2 laser.
2. Description of the Related Art
FIG. 3 shows an arrangement of a conventional CO.sub.2 laser which includes an electric discharge tube 1 having an output coupling mirror 2 and a total reflection mirror 3 that are positioned at opposite ends of the electric discharge tube 1. Two metal electrodes 4 and 5 are arranged on the outer circumference of the electric discharge tube 1, and when a high-frequency voltage is applied between the metal electrodes 4 and 5 from a high-frequency power supply 6, a high-frequency glow discharge is produced in the electric discharge tube 1 for laser excitation. A laser beam axis in the electric discharge tube 1 is indicated at 13, and a laser beam axis extending out of the tube 1 from the output coupling mirror 2 is indicated at 14.
To start the laser oscillator device, a gas in the device is first evacuated by a vacuum pump 12, and then a valve 11 is opened to introduce a predetermined amount of laser gas from a gas container 10 into the device until the pressure of the gas in the device reaches a prescribed pressure level. Subsequently, the device is continuously evacuated by the vacuum pump 12 and continuously replenished with the laser gas through the valve 11. The laser gas in the device is therefore continuously replaced with a fresh gas while the gas pressure in the device is kept at the prescribed pressure level, and accordingly, contamination of the laser gas in the device is prevented.
In FIG. 3, the laser gas is circulated in the device by a Roots blower 9, whereby the laser gas is cooled. In a CO.sub.2 laser, about 20% of the applied electric energy is converted into a laser beam and the rest is consumed to heat the laser gas, but theoretically, since the gain of laser oscillation is proportional to the minus (3/2)th power of the absolute temperature T, it is necessary to forcibly cool the laser gas to increase the oscillation efficiency. In the illustrated device, the laser gas flows through the electric discharge tube 1 in the direction indicated by the arrows at a speed of about 100 m/sec., and is introduced into a cooling unit 8. The cooling unit 8 removes most of the heat energy produced by the electric discharge from the laser gas. Further, since the Roots blower 9 heats the laser gas when compressing same, the laser gas from the Roots blower 9 is passed through a cooling unit 7 before the laser gas is again introduced into the electric discharge tube 1. The cooling units 7 and 8 will not be described in detail as they are well known in the art.
The above conventional laser oscillator device has the following problems: First, since the Roots blower is a low-speed volumetric blower, it is large in size and weight, and thus the laser oscillator itself is large; second, the Roots blower emits a pulsating gas flow, and the laser oscillation characteristics are affected by this pulsating gas flow; and third, the Roots blower produces vibrations which adversely affect the spot positioning stability of the laser beam.
If a turbo blower is used instead of a Roots blower, however, it may be damaged due to resonance when rotated at a high speed.